1. Field of the Invention
The present invention is directed to an intake air pressure sensor assembly for an internal combustion engine, and in particular, a fuel-injected engine that communicates with a controller for controlling the fuel injectors and ignition timing based on detected air pressure fluctuations.
2. Background Art
In all fields of engine design there is emphasis on fuel economy, engine performance, and most notably, engine-out emissions. Increased emissions restrictions have led to the necessity of a more accurate fuel metering process. Fuel injection systems have emerged as an accurate way to control the air and fuel mixture in an internal combustion engine and thus keep emissions low. The trend towards fuel injection has not been without added costs, and as such has limited the applications of this technology in price sensitive markets. To apply fuel injection to an engine, one must add an engine controller, a more complex fuel system, and multiple sensors. In addition, engines often need to be redesigned to allow for the application of these control electronics. All of these components add costs and complexity to the engine system. Many manufacturers simply cannot be competitive with the added costs of fuel injection in their product line, and as such are delaying its implementation until emissions regulations mandate its use. It would be ideal to have an accurate system for controlling an internal combustion engine that is less complex and less costly to implement on current engine technology.
A four-stroke engine must rotate two complete rotations for one full engine cycle. This cycle is comprised of the intake, compression, power, and exhaust strokes. The four-stroke cycle is based on a 720° cycle, or two complete rotations of the crankshaft. In relation to four-stroke engines, the engine phase determines which half of the 720° cycle the engine is on. For example, if a four-stroke engine is “in phase” on a 720° cycle, it is considered synchronous, and the engine controller can correctly determine which stroke the engine is on. If the four-stroke engine is not synchronous, the engine controller can only determine engine position on a 360° cycle. Many systems must determine engine phase to obtain the appropriate timing on four-stroke engines. A two-stroke engine must only rotate one complete rotation for a complete engine cycle. No phase information must be obtained from this engine cycle. This will be referred to as a 360° engine cycle.
Typically, a fuel injection system utilizes a plurality of sensors on the engine to determine engine operating conditions. For example, a fuel-injected engine may be equipped with a crankshaft position sensor, cam position sensor, intake air pressure sensor, and barometric air pressure sensor in addition to other sensors. The engine controller monitors these sensory inputs to determine the appropriate ignition timing, injection timing, and quantity of fuel to be injected. It would be beneficial to reduce the number of sensors necessary to operate an engine, yet maintain accurate control. This would result in fewer components, less complexity, and reduced costs.
One of the various types of data monitored by these sensory inputs to the engine controller is the determination of the intake air pressure. This measurement process can be quite complex. This challenge can be complicated further by monitoring intake air pressure in engines with few cylinders. It is well known in the art that intake pressures fluctuate with the opening and closing of the intake valves during the intake stroke. If there is a plurality of cylinders there will be more intake events per crankshaft rotation and traditionally less overall intake air pressure fluctuations. However, if few cylinders are present as in small engines, there will be fewer intake events per crankshaft rotation and large intake air pressure fluctuations will be apparent. If the average intake pressure were to be obtained, it will not be an accurate indication of actual cylinder intake air pressures due to these fluctuations.
Air pressure sensors have been used in the calculation of intake air mass seen by reference to U.S. Pat. No. 6,453,897 to Kanno. In this approach, the intake air pressure of the engine is sampled just once per engine crankshaft revolution. It is generally understood in the art that the air pressure can be used for intake air mass calculations in fuel injection control. Kanno presents a system that has increased accuracy for measuring intake air pressure and therefore increased accuracy in obtaining intake air flow rate and desired air/fuel ratio in the engine. This example presents no applications to determining engine phase or crankshaft position through the air pressure fluctuations. Instead, this approach strictly pertains to a single air pressure measurement at a predetermined crankshaft position. The timing of this measurement is determined through the use of a crankshaft position sensor and engine control unit.
In some applications, the mass air flow rate into the engine is estimated in part by measuring the absolute pressure within the induction manifold (Manifold Absolute Pressure, or “MAP”). A mass air flow rate is the mass of air drawn into an engine over a particular period of time. Air density, or mass per unit volume, is proportional to air temperature, pressure, and humidity of the air drawn into the engine. This data is used to calculate the mass air flow rate of the engine, or mass of the incoming air. Such calculations are known as volume-density or speed density calculations.
With crankshaft position measurement, a toothed wheel is typically used in conjunction with a pickup to detect positional movement. These devices are traditionally hall effect devices or variable reluctance devices. In automotive applications, the toothed wheel consists of multiple teeth or “timing slugs” evenly spaced on the crankshaft. The number of teeth is traditionally a whole divisor of 360°. As the number of teeth is increased, resolution of the system is increased. In many applications, there is a missing tooth to indicate a predetermined position on the crankshaft itself. An automotive standard of today is known as a “36-1” pattern. This pattern evenly spaces 36 gear teeth on a ring, and has one of the 36 teeth removed to indicate a predetermined angular position. From this input, engine rpm and crankshaft position can be directly measured. Unfortunately, the crankshaft rotates twice for a complete 720° cycle in four stroke engines. A crankshaft position sensor can not indicate engine phase on a four-stroke engine because of this. The crankshaft will be in the exact same position twice during the engine cycle. Additional sensory information is required to synchronize to a 720° cycle, if the engine controller is to operate in a synchronous manner. If the crankshaft is keyed to indicate its position, it is only possible to determine engine position based on 360° cycle, or a single crankshaft rotation without additional sensory information.
Many small engines utilize a crankshaft trigger mechanism for indicating a predetermined crankshaft position for ignition purposes. With this mechanism an ignition spark is emitted every 360° of crankshaft rotation. This type of system is similar to a crankshaft position sensor with the distinction of having only a single signal indicating pulse per crankshaft revolution. A system of this nature typically is not in communication with an engine control device, but is rather part of a stand-alone ignition system. As such, there is little or no memory from one cycle to the next. These systems cannot predict engine timing for fuel injection purposes due to crankshaft acceleration and deceleration. They can however consistently trigger an ignition system at a fixed crankshaft angular position.
To determine engine phase on four stroke engines, an additional sensor is typically used in conjunction with a crankshaft position sensor. A camshaft position sensor may be used to determine an engine's phase. The camshaft rotates at exactly half the speed of the crankshaft and they are mechanically linked. Therefore, these two sensory inputs provide the engine controller with engine position information to run on a synchronous basis to a 720° engine cycle. Due to its nature, a camshaft position sensor is not as accurate as a crankshaft position sensor and therefore they are typically used in combination.
In most applications, these are all discrete and separate sensors. Each sensor traditionally has only a single role in monitoring engine conditions. They each require their own wiring, connectors, and tooling to be mounted to the engine. These multiple parts all add in the cost of fuel injection implementation.
Additionally, if the crankshaft position sensor were to fail for any reason, little or no redundancy is implemented and the engine would cease to operate.
It would be advantageous to reduce the number of sensors necessary to run the engine. If this could be done, cost savings would be realized in fewer sensors, reduced tooling, reduced fixturing, reduced assembly time, and lower design costs. If fewer sensors were required to accurately control fuel injection timing, it would enable a more cost efficient transition of non-fuel injected engines to the technology.
Accordingly, several objects and advantages of my invention are the multiple uses of a single intake pressure sensor to control the timing of an internal combustion engine and measure intake air mass. This invention was designed for use on a single cylinder engine, but may be applicable to, but without limitation to, all forms of internal combustion engines exhibiting intake pressure fluctuations. This invention reduces the number of sensors necessary to determine engine timing and operating characteristics by monitoring intake pressure fluctuations.
To effectively time an engine, this invention can replace the crankshaft position sensor, cam position sensor, manifold air pressure sensor, and barometric pressure sensor with a single part. With this technology a single intake air pressure/temperature sensor could be used as a stand-alone mechanism for fuel metering and injection timing. By monitoring the intake pressure fluctuations, one would observe a vacuum pulse every two crankshaft rotations (in a four stroke engine, once per revolution in a two stroke engine). This is indicative of a particular crankshaft position and the time when the intake valve is open. When implemented with a microprocessor, the time interval between intake pressure events could be mathematically modeled to predict when the next event would occur. In addition, this model could offer a prediction of crankshaft position sub-cyclic to the intake pressure events. With this timing information, fuel metering and ignition timing could accurately and precisely be added to an engine in a non-intrusive form. No additional sensors need to be hard tooled or machined into the engine block material. This may be of specific benefit to companies that want to add fuel injection technology to an existing product. This system, while not having resolution as high as a “36-1” tooth crank position pick-up on an automobile engine, offers excellent accuracy at much lower costs.
Many small engines of today use some form of crankshaft trigger for their ignition system. If a crankshaft trigger or crankshaft position sensor input were combined with the technology of this patent, increased accuracy and resolution would be obtained in engine timing. Using a crankshaft trigger alone does not allow an engine to be timed on a 720° cycle (in four stroke applications). With the input of the intake pressure fluctuations in addition to a crankshaft trigger, and engine may be aligned in phase on a 720° cycle. When implemented with a microprocessor, the system can be mathematically modeled to predict and monitor intake pressure events. With this information, a much higher resolution can be obtained than in the previous example. With this timing information, fuel metering and ignition timing could accurately and precisely be added to an engine in a non-invasive form.
Redundancy is obtained in a system of this nature. If one of the two sensors were to fail, the other sensor would provide ample signal to enable the engine to continue to be operated, with reduced resolution. This may be a valuable benefit if the engine were to be placed into a vehicle where engine failure cannot be tolerated in the field.
Due to the location of the pressure sensor in the intake tract, this allows for engine manufacturing to be simplified. Tooling, engineering, and design time does not have to be invested in placement of multiple sensors in the engine castings. This control system specifically benefits manufacturers who may want to add fuel injection to an existing carbureted product. The non-invasive nature of this invention lends itself to applications in engines where tooling, packaging, or redesign costs are too high to consider standard fuel injection applications.
Further objects and advantages of my invention will become apparent from a consideration of the drawings and ensuing description.